Summary Activation of transcription is the ultimate endpoint for many signal transduction and developmental pathways, and understanding the mechanism of activation is a key to understanding gene regulation. From previous studies, it is clear that disruption of normal gene regulation by mutations in gene- specific transcription activators and coactivators can lead to cancer and other diseases. The broad long- term objectives of this proposal are to determine the mechanisms used by gene-specific activators and coactivators to regulate RNA polymerase II transcription. The proposed work will provide a basis for understanding gene regulation in normal and diseased states at the molecular level. The specific aims of this work utilize biochemical, structural, and molecular genetic methods to examine the direct targets of two activation domains and two coactivators. We will examine the structure of several acidic activator-coactivator complexes to understand how activators specifically recognize their targets, common principals of activator-target recognition and, more generally, the function of intrinsically disordered proteins. We will examine the interaction of the SAGA coactivator with TBP (TATA binding protein) and how this interaction is regulated by acetylation. Using a unique set of crosslinking reagents, we will examine the direct targets of the Mediator coactivator complex within the transcription machinery. In all cases, we will use yeast molecular genetics to test the functional significance of our biochemical results. Combined, our results will lead to a molecular model for how activators recognize their coactivator targets and how coactivators stimulate gene expression by direct interaction with the transcription machinery.